The present invention relates to a closure system for containers, in particular for non-returnable containers of semi-rigid material preferably a metal-plastic composite material in the form of dish-shaped parts with outward facing flanges joined by a sealed seam, the container being in particular for holding liquid and/or pasty, or granular and/or powder-like substances such as chemicals for example.
For such containers made of semi-rigid material and of larger dimensions, it can be useful if, after the flanges of the metal-plastic composite dish-shaped parts have been joined by at least one sealed seam, these flanges are bent over and held in the bent over position by means of a holding device. This bent over position of the flange is at least conducted in a previous special step, the degree of bending being further increased, for example until the flange is flat, by means of the holding device. Usefully, the holding device can be in the form of a protective packaging made of cardboard or pre-shaped, foam material, or else by a sleeve, in order to keep the sealed flanges of the container dish-shaped parts in a bent position.
It has been found particular favorable to make such non-returnable containers out of an aluminum-plastic composite in which the aluminum foil or strip of the composite is 10-250 .mu.m thick, preferably 20-160 .mu.m thick.
Conventional rigid closing devices e.g. with screw tops or lids are unsuitable for such containers made of semi-rigid material, as the rigid material of the closure very often causes overloading of the surrounding semi-rigid container wall and produces cracks or tears in it. This is also the case when such containers are inserted in a protective packaging of rigid material. A conventional closure of rigid material would project above the container wall and, if accidentally knocked e.g. if the package were dropped, would come against the inside of the protective packaging and deform and break the surrounding, unsupported area of the container wall. It was therefore necessary to develop a closure system which is compatible with the material of the container wall and, furthermore, is as flat as possible.
A further problem is to minimize as far as possible any reduction in the strength of the container by provision of a closure system, and therefore to design the opening for filling such that it is as small as possible. In spite of this there must be the possibility for the user of the contents to be able to remove the contents from the container without difficulty.
Such containers of semi-rigid material are, furthermore, usefully manufactured on a packaging line by joining matching dish-shaped container halves by heat sealing, such dish-shaped halves being produced with a slightly conical cross section by deep drawing. For reasons of manufacture it may also be necessary to store these dish-shaped parts by stacking them inside each other. It is then also desirable for the dish-shaped parts, i.e. at least one of the pair, to be provided with its closure device before being stored. Conventional closures, however, project out from the wall and would therefore make it impossible to stack container halves fitted with such closure systems. For this reason also it is desirable for the closure to be as flat as possible.
The object of the invention is therefore to produce a closure system which meets these various requirements.